I've just had a look at my car Graham and would say the new holes look to be in the same position as your old bracket, so those two fixings are indeed captive in the crossmember.
I'll take a photo if I can get my camera to work (one of the terminals is corroded and it is awkward to get at it) when I have more time.
I may also have a go at removing mine as they're very rusty like yours. The heads of those bottom bolts are not easy to see either, in fact I can't quite see or feel them.
Gave up with the camera, this is one from my very rubbish phone, forgive the quality. Now it looks like it has had a bit added to the top, I'll have to check to see if this is actually required.

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